Hologram plate and its fabrication process

ABSTRACT

The invention provides a hologram plate which is used with the double-focus replication process, and which is integrated with a spacer to impart marring resistance thereto, and is integrated with a light absorbing layer to allow zero-order light and first-order light to have substantially the same intensity. This hologram plate  42  comprises an array of collective element holograms for diffracting parallel light incident thereon at a specific wavelength and a specific incident angle in such a way that the light is converged onto a specific focal length position. The hologram plate  42  is a multilayer structure made up of a first transparent substrate  31,  a hologram layer  32,  an adhesive layer  33  and a second transparent substrate  41.  The second transparent substrate  42  defines a surface in contact with a hologram photosensitive material  53  during hologram replication.

BACKGROUND OF THE INVENTION

The present invention relates generally to a hologram ate and itsfabrication process, and more specifically to a hologram plate designedto replicate a hologram array comprising collective element hologramssuch as hologram color filters, and its fabrication process.

The present invention is also concerned with a multifaceted hologramplate and its fabrication process.

Further, the present invention is directed to the construction of aprotective film for a hologram plate.

In JP-A 06-222361, etc., the applicant has already come up with ahologram-harnessing color filter for the purpose of greatly increasingthe efficiency of utilization of liquid crystal display backlights, etc.This hologram color filter is basically made up of an array of atransmission type of collective element holograms capable of diffractingparallel light incident thereon at a specific wavelength and a specificangle of oblique incidence in such a way that it is converged on aspecific focal distance position.

To use such a hologram array as a hologram plate to replicate anotherhologram array having similar properties by a hologram replicationprocess, for instance, a first hologram plate is fabricated in the formof a computer-generated hologram (CGH). Then, the first hologram plateis replicated by the hologram replication process to fabricate ahologram plate, from which the final product is fabricated by a similarhologram replication process.

To replicate such a transmission type of collective element hologramarray as mentioned above, the applicant has filed a patent application(JP-A 09-90860) to come up with a process wherein when replicas of thefirst plate and hologram plate are fabricated, the distance between thehologram plate and a hologram photosensitive material is fixed tosubstantially double the focal length of each element hologram to make ahologram replica having similar properties to those of the hologramplate. This process is now explained with reference to FIG. 12.

FIG. 12 is illustrative of how to fabricate a hologram array 5 providinga hologram color filter from a CGH array plate 7 in one singlereplication operation. A plate for a hologram array 5 providing ahologram color filter is constructed in the form of a CGH array 7. Thedistance from the relief surface of the CGH array plate 7 to aphotosensitive layer 13 is fixed to 2 f that is double the focal lengthf of each CGH 5″ so that a hologram photosensitive material 8 is spacedaway from the CGH array plate 7. Laser light 9 having a specificwavelength is entered into the CGH array plate 7 at a specific angle ofincidence, so that diffracted light 10, converged by the diffractionaction of each CGH 5″ from convergent light to divergent light, andstraightforwardly traveling transmitted light 11 interfere in thephotosensitive layer 13 of the hologram photosensitive material 8.

Here let D represent the diameter of a recording area of each elementhologram 5″ of the CGH array plate 7. Then, the diffracted light 10,once converged on a position P located at a distance f from the reliefsurface of each CGH 5″, is converged on a 2 f position into a divergentlight beam having the same diameter D. Accordingly, if the divergentlight and the straitghtforwardly traveling transmitted light 11interfere in the photosensitive layer 13 located at this position, thediameter of the hologram interference fringe recording area becomesequal to D, and the pitch between adjacent replicated element hologramsbecomes equal to that between adjacent element holograms 5″ of the CGHarray plate 7 as well. In addition, when light traveling in the oppositedirection to the transmitted light for hologram array replication isentered in the thus replicated hologram array from the glass substrate12 side, the diffracted light is converged on a position P at a length ffrom the photosensitive layer 13 with hologram interference fringesrecorded therein, and so has the same diameter as the focal length ofeach element hologram 5″ of the CGH array plate 7. In other words, ahologram array completely identical with the CGH array plate 7 isobtained.

The hologram array replicated from the CGH array plate 7 in such anarrangement as shown in FIG. 12 is then used as a hologram plate toobtain the end product. FIG. 13 is illustrative of one arrangement ofhow to carry out such second replication operation. In FIG. 13, H1stands for an intermediate hologram array obtained by replication in thearrangement of FIG. 12. This intermediate hologram array H1 is againused as a hologram plate for replication purposes. In this case, thehologram photosensitive material 8 is located on the side of the plate 7for the replication of the intermediate hologram array H1, andreconstructing illumination laser light 9′ is entered in theintermediate hologram array H1 from the opposite direction to thetransmitted light 11 for the replication of the intermediate hologramarray H1, and the distance from the diffraction surface of theintermediate hologram array H1 to the photosensitive layer 13 of thehologram photosensitive material 8 is fixed to 2 f that is double thefocal length f of each element hologram. When the reconstructingillumination laser light 9 is entered in the intermediate hologram arrayH1 in such an arrangement, light 10′ diffracted by each element hologramof the intermediate hologram array H1 travels in the opposite directionto the diffracted light 10 of FIG. 12 and, once converged, is convertedat the 2 f position to a divergent light beam having the same diameterD. Accordingly, diffracted light 10′ and straightforwardly travelingtransmitted light 11′ interfere in the photosensitive layer 13 locatedat this position as in the case of FIG. 12, so that an array of elementholograms having the same focal length f is replicated and recorded at apitch d in the area having the same diameter D.

The feature of this process is that a hologram similar in properties tothe hologram plate can be fabricated even when the hologram plate is inno perfect contact with the replica. In what follows, the hologramreplication process in such an arrangement will be called a double-focusreplication process.

Incidentally, hologram photosensitive materials such as photopolymersare generally poor in marring resistance whether in an unrecorded stateor in a state subjected to post-recording treatments. When replicationis carried out with a hologram plate in close contact with a hologramphotosensitive material, it is likely that the hologram on the hologramplate side is immediately damaged and some of the photosensitivematerial on the replication side peels off, depositing onto the hologramon the hologram plate side. Such depositions are hardly removable.

When a hologram has such a focal length as mentioned above, there is avariation in the focal length of replicas due to a contact gap at thetime of replication, and a variation in gap thickness leads to avariation in the focal length of replicas.

It is desired that the zero-order light and first-order light diffractedby the hologram plate have substantially the same intensity at theposition of the hologram photosensitive material. To this end, it isrequired to place the refractive index modulation under severe control.However, this control is difficult on practical levels.

The hologram (intermediate hologram array HI) used for the replicationof the end products is herein called the hologram plate. When a hologramplate having only one hologram (hologram color filter) equivalent to onesegment is used for the replication of such a color filter as mentionedabove, however, replication efficiency becomes worse.

To avoid this, a process has been proposed in the art, which processmakes use of a hologram plate obtained by translating a CGH plate 7 withrespect to one large hologram photosensitive material 8 for a pluralityof replication cycles wherein, for instance, four or eight holograms areexposed to light to form four or eight juxtaposed holograms in thehologram photosensitive material, so that four or eight holograms can besimultaneously replicated in one replication operation. Such a hologramplate with a plurality of juxtaposed holograms is called a multifacetedhologram plate.

As shown in FIG. 13, for instance, the multifaceted hologram plate isprepared in plural replication operations, using a CGH plate withrespect to one large hologram photosensitive material. However, when atleast one of plural exposure operations (replication operations from theCGH plate) is improper, the resultant multifaceted hologram plate cannotbe used or fails to provide a hologram plate having good replicationefficiency.

In view of such prior art states as mentioned above, the first object ofthe present invention is to provide a hologram plate used with thedouble-focus replication process, which is integrated with a spacer toimpart marring resistance thereto, and is integrated with a lightabsorbing layer to allow zero-order light and first-order light to havesubstantially the same intensity, and its fabrication process.

The second object of the present invention is to provide a multifacetedhologram plate which can have hologram segments of improved properties,can be used for efficient replication, and has improved durability, andits fabrication process.

The third object of the present invention is to provide an easilyreleasable protective film for a hologram plate, which prevents surfacemarring, wearing and contamination at the time of contact replication orremoval of foreign matters.

SUMMARY OF THE INVENTION

According to the present invention, the aforesaid first objet isachieved by the provision of a hologram plate comprising an array of atransmission type of collective element holograms that diffract parallellight incident thereon at a specific wavelength and a specific angle ofincidence in such a way that the parallel light is converged on aspecific focal length position, characterized by comprising a multilayerstructure made up of a first transparent substrate, a hologram layer, anadhesive layer and a second transparent layer, said second transparentsubstrate defining a surface into contact with a hologram photosensitivematerial when hologram replication is carried out.

Preferably in this case, the second transparent substrate should have athickness that is substantially twice the focal length of eachcollective element hologram, inclusive of the thickness of the adhesivelayer.

Preferably, a water-soluble protective layer should be interleavedbetween the hologram layer and the adhesive layer.

Preferably in the case mentioned just above, the second transparentsubstrate should have a thickness that is substantially twice the focallength of each collective element hologram, inclusive of the thicknessesof the adhesive layer and water-soluble protective layer.

The diffraction efficiency of the hologram layer may be preset in such away as to allow the zero-order light and first-order light diffracted bythe hologram layer to have substantially the same intensity.

An absorbing layer may be interleaved at any desired position betweenthe hologram layer and the second transparent layer, and a lightabsorbing material is dispersed throughout the absorbing layer in such away as to allow the zero-order light and first-order light diffracted bythe hologram layer to have substantially the same intensity.

An absorbing layer may be located on the surface of the secondtransparent substrate, and a light absorbing material is dispersedthroughout the absorbing layer in such a way as to allow the zero-orderlight and first-order light diffracted by the hologram layer to havesubstantially the same intensity.

According to the present invention, there is also provided a process forfabricating the hologram plate for the purpose of achieving theaforesaid first object of the present invention, characterized in that:

said adhesive layer comprises an ultraviolet curing adhesive agent,

said multilayer structure, obtained by forming said hologram layer onsaid first transparent substrate and then superposing said secondtransparent substrate on said hologram layer with an uncured ultravioletcuring adhesive agent interleaved therebetween, is spun to spin an extraportion of said adhesive agent out of the periphery thereof, therebymaking said adhesive layer uniform, while the rpm of said multilayerstructure is controlled to obtain a desired thickness, and

said multilayer structure is irradiated with ultraviolet radiationthrough said first transparent substrate or said second transparentsubstrate to cure said adhesive agent.

Preferably in this case, the hologram layer is exposed to p-polarizedlight. P-polarized light is more reduced in interface reflection thans-polarized light, so that unnecessary interference fringes can bereduced during exposure and Δn (refractive index modulation) can becontrolled to a reduced value as well.

However, when the diffraction efficiency of the CGH plate is too low asan example, the use of s-polarized light is preferable because Δn can beincreased with an increased diffraction efficiency.

In the present invention for the purpose of achieving the aforesaidfirst object, the hologram plate comprises a multilayer structure madeup of a first transparent substrate, a hologram layer, an adhesive layerand a second transparent layer and the second transparent substratedefines a surface in contact with a hologram photosensitive materialduring hologram replication, so that the second transparent substratecan function as a protective layer to make the hologram plate resistantto marring. In addition, the second transparent substrate can be used asa spacer for a double-focus replication process wherein the distancebetween the hologram plate and the hologram photosensitive material isset at substantially double the focal length of each collective elementhologram, so that replicas can be fabricated with constant focallengths.

An absorbing layer is located between the hologram layer and theadhesive layer or at other position to allow the zero-order light andfirst-order light diffracted by the hologram layer to have substantiallythe same intensity, so that hologram replicas of high diffractionefficiency can be obtained.

The present invention has been described with reference to thedouble-focus fabrication process. It is noted, however, that it isactually important and desirous to keep the distance between thehologram plate and the photosensitive material constant in considerationof the total thickness of all members inclusive of the adhesive layer,protective layer and index matching liquid.

When the first replication is carried out in the contact mode and thesecond is carried out by the double-focus replication process, it isdesired that the distance coincide with the value obtained by thesubtraction of the first replication gap from the value double the focallength.

The aforesaid second object of the present invention is achieved by theprovision of a hologram plate comprising a plurality of juxtaposed unithologram segments, characterized in that:

one common transparent thin sheet is provided over the surfaces of saidplurality of juxtaposed unit hologram segments with an adhesive agentinterleaved therebetween.

Preferably in this case, each unit hologram segment should comprise atransparent substrate, a photosensitive material layer formed thereonwhile a hologram is recorded therein, and a protective layer formed onsaid photosensitive material layer.

It is here preferable that a transparent thin sheet should be bondedonto said protective layer for each unit hologram segment.

It is also preferable that said plurality of unit hologram segmentsshould be hologram segments replicated from the same hologram plate.

Each unit hologram segment, for instance, may be a hologram colorfilter.

Regarding the aforesaid second object of the present invention, there isprovided a process for fabricating a hologram plate comprising aplurality of juxtaposed unit hologram segments and one commontransparent sheet provided over the surfaces of said unit hologramsegments with an adhesive agent interleaved therebetween, characterizedby comprising steps of:

preparing a plurality of unit hologram segments,

adsorbing a transparent thin sheet onto the surface of a reference plateand laminating said plurality of unit hologram segments, in juxtaposedrelation to each other, on said transparent thin sheet with an adhesiveagent interleaved therebetween,

bonding a base plate onto the back side of said plurality of juxtaposedunit hologram segments with an adhesive agent interleaved therebetween,and

desorbing said transparent thin sheet from said reference plate torelease said transparent thin sheet from said reference plate.

Preferably in this process, at the step of preparing a plurality of unithologram segments, said plurality of unit hologram segments arereplicated from the same hologram plate.

According to the present invention for achieving the aforesaid secondobject, all the unit holograms can be precisely replicated because theunit hologram segments are kept flush with one another by one commonthin sheet glass provided over the plurality of juxtaposed unit hologramsegments. When the hologram photosensitive material is brought intoclose contact with the multifaceted hologram plate with an indexmatching liquid applied therebetween for the purpose of hologramreplication, it is extremely unlikely that an optical adhesive agentbetween adjacent unit hologram segments will be dissolved in the indexmatching liquid. If a glass sheet is used as the transparent thin sheet,improved durability is then obtained. Fabricated by the lamination ofonly unit hologram segments put in good alignment with good properties,the multifaceted hologram plate according to the present invention forachieving the aforesaid second object have all unit hologram segments ofgood quality and uniform properties, and so can be used for hologramreplication with high efficiency.

According to the present invention for achieving the aforesaid thirdobject, there is provided a hologram plate comprising a hologram layerwith interference fringes formed thereon, a first layer capable of beingremoved with water or a solvent, which is provided on the surface ofsaid hologram layer or a transparent layer formed thereon, and a secondlayer of a curing resin capable of being cured by light or heat, whichis formed on said first layer.

In this hologram plate, the hologram layer may be either an amplitudetype hologram layer with a metal film patterned thereon or a hologramlayer comprising a hologram photosensitive material layer withinterference fringes recorded therein.

The first layer may have the property of absorbing light.

This hologram plate may be applied to either a transmission typehologram or a reflection type hologram.

Thus, the hologram plate for achieving the aforesaid third object of thepresent invention comprises a hologram layer with interference fringesformed thereon, a first layer capable of being removed with water or asolvent, which is provided on the surface of said hologram layer or atransparent layer formed thereon, and a second layer of a curing resincapable of being cured by light or heat, which is formed on said firstlayer. The second layer functions as a protective layer for the hologramlayer 202, thereby preventing the marring, wearing and contamination ofthe hologram layer, which may otherwise occur at steps of coating anindex matching liquid, carrying out contact replication, removing theindex matching liquid, removing foreign matters, and so on. As manyholograms are replicated, the second layer, too, is subjected tomarring, wearing and contamination. In this case or, for instance, whenone fails to form the first layer or the second layer, the hologramplate is washed with water or boiled in boiling water, so that theprotective layer can be easily removed. Then, if fresh first and secondlayers are provided on the hologram layer, the hologram plate can beregenerated.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrative of an arrangement of how to replicate a hologramfrom a CGH array plate according to the first embodiment of theinvention.

FIG. 2 is illustrative of an arrangement of how to fabricate a hologramplate according to the first embodiment from the hologram replica ofFIG. 1.

FIG. 3 is illustrative of an arrangement of how to fabricate the endhologram replica from the hologram plate of FIG. 1 by the double-focusreplication process.

FIG. 4 is illustrative of an arrangement of how to fabricate a hologramplate according to the second embodiment from the hologram replica ofFIG. 1.

FIG. 5 is a sectional view of the first step of the process forfabricating a hologram plate for the purpose of achieving the secondobject of the invention.

FIG. 6 is a sectional view of a step subsequent to FIG. 5.

FIG. 7 is a sectional view of a step subsequent to FIG. 6.

FIG. 8 is a sectional view of a step subsequent to FIG. 7.

FIG. 9 is a sectional view of a step subsequent to FIG. 8.

FIG. 10 is a sectional view of a multifaceted hologram plate accordingto one embodiment of the invention.

FIG. 11 is illustrative of how to fabricate a transmission type hologramusing the hologram plate of the invention for the purpose of achievingthe third object of the invention.

FIG. 12 is illustrative of an arrangement of how to fabricate a hologramreplica from a CGH array plate by a conventional double-focusreplication process.

FIG. 13 is illustrative of an arrangement of how to again makereplication using a hologram replica obtained in the arrangement of FIG.12 as a hologram plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the hologram plate according to the present invention andits fabrication process are now explained.

In the first embodiment of the present invention, the first hologramplate was fabricated in the form of a relief type computer-generatedhologram (CGH) comprising an array of a transmission type of divergentelement holograms. To fabricate this relief type CGH, the inferencefringes of the divergent element holograms were first computed by meansof a computer in such as a way that laser light of 488 nm wavelength,incident thereon at an incident angle of 40°, was diverged from a 50 μmfocal length position on the incident side. Then, the interferencefringes were rendered by means of electron beams on the surface of aglass substrate on which, for instance, an electron beam resist wascoated, followed by development. In FIG. 1, the CGH array plate is shownat 21, the element holograms at 22, and a relief surface at 23.

On the other hand, a hologram photosensitive material in the form of aphotosensitive material 32, viz., photopolymer HRF600X made by Du Pontwas applied onto a glass substrate 31, viz., a 1737 glass substrate of1.1 mm in thickness, made by Corning, thereby obtaining a hologramphotosensitive material 33.

If required, a water-soluble protective layer formed of PVA (polyvinylalcohol), etc. may be coated on the photosensitive layer 32. Thisprotective layer acts as a barrier layer for preventing the adhesivelayer 37 to be referred to later from diffusing into the photosensitivelayer 32, resulting in adverse influences such as a lowering of thedegree of refractive index modulation, the swelling of the interferencefringes, etc.

Then, the photosensitive layer 32 of the hologram photosensitivematerial 33 was brought into close contact with the relief surface 23 ofthe CGH array plate 21. P-polarized argon laser light 34 of 488 nmwavelength was entered at an incident angle of 40° into the resultantmultilayer structure from the back side of the CGH array plate 21(facing away from the relief surface 23) to allow divergent diffractedlight 35 diffracted by each element hologram 22 of the CGH array plate21 to interfere with straightforwardly traveling transmitted light 36 inthe photosensitive layer 32 of the hologram photosensitive material 33,thereby replicating a hologram from the CGH array plate 21. If, in thiscase, p-polarized light is used as the laser light 34, it is thenpossible to reduce reflections at the interface between the hologramphotosensitive material 33 and the plate 21, the interface between thehologram photosensitive material 33 and air, etc., thereby preventingunnecessary interference fringes from being recorded.

After the photosensitive layer 32 had been exposed to light in a givenfashion, an adhesive agent, viz., an ultraviolet curing adhesive agent37 and a glass plate 41 acting as a spacer were placed on thephotosensitive layer 32, as shown in FIG. 2. Then, the resultantmultilayer structure was spun by means of a spinner to spin an extraportion of the adhesive agent 37 out of the periphery thereof, so thatthe adhesive layer 34 was made uniform, while the rpm of the spinner wascontrolled to obtain the desired thickness. In this way, the glass plate41 was laminated on the photosensitive layer 32. Glass D263 of 100 μm inthickness, made by Shot, was used for the glass plate 41 and the spinnerwas spun at a fixed 2,800 rpm.

Thereafter, the adhesive agent 37 was cured by ultraviolet irradiationthrough the glass substrate 31 or the glass plate 41.

Then, the end product was obtained by the aforesaid double-focusreplication process from the thus obtained hologram plate 42 comprisinga hologram array integrated with the spacer glass plate 41. FIG. 3 isillustrative of an arrangement of how to carry out such secondreplication operation. According to the arrangement of FIG. 3, thehologram array 33 integrated with the spacer glass plate 41 by means ofthe adhesive agent 37 is used as the hologram plate 42, and aphotosensitive material 53 is prepared by the application onto a glasssubstrate 51 of a hologram photosensitive material in the form of aphotosensitive layer 52, viz., photopolymer HRF600X made by Du Pont. Thephotosensitive layer 52 of the hologram photosensitive material 53 isbrought into close contact with the spacer glass sheet 41 of thehologram plate 42. Then, p-polarized argon laser light 54—that has thesame wavelength as that of the illumination light 34 for the replicationof the hologram array of hologram plate 42 and travels in the oppositedirection thereto—is entered at the same incident angle of 40° into thehologram plate 42 now from the glass substrate 31. Then, diffractedlight 55—that is diffracted by each element hologram of the hologramplate 42 and diverged upon converging onto the focal point—is allowed tointerfere with straightforwardly traveling transmitted light 56 in thephotosensitive layer 52 of the hologram photosensitive material 53 forreplication purposes. The p-polarized light is used for the same reasonas mentioned above. In the embodiment, each element hologram of thehologram array of hologram plate 42 has a focal length of 50 μm whereasthe spacer glass plate 41 has a thickness of 100 μm that is just doublethe focal length of each element hologram of the hologram plate 52.Thus, the focal length of each element hologram of the replica, too, canbe regulated to accurately 50 μm by the double-focus replicationprocess.

More preferably in this embodiment, the thickness of the spacer glassplate 42 inclusive of the thickness of the adhesive agent 37 and thethickness of the absorbing layer 57 (FIG. 4) to be referred to latershould be just double the focal length of each element hologram.

The hologram plate 42 used with such a double-focus replication process,because of using the glass plate 41 as the spacer, was so improved interms of marring resistance that it could be used for hologramreplication over and over. In the process of hologram replication, someof the hologram photosensitive material 53 was deposited onto thehologram plate 42. However, this hologram plate 42 could easily bewashed by conventional scrubbing without causing damage thereto.

The second embodiment of the invention is now explained. As shown inFIG. 1, the CGH array plate 21 is used as the hologram plate 42. As inthe first embodiment, divergent diffracted light 35 diffracted by eachelement hologram 22 in the CGH array plate 21 is then allowed tointerfere with straightforwardly traveling transmitted light 36 in thephotosensitive layer 32 of the hologram photosensitive material 33 tofabricate a hologram replica of the CGH array plate 21. After exposureof the photosensitive layer 32 to light in a given fashion, as shown inFIG. 4, the photosensitive layer 32 was coated thereon with aconcentration-controlled polyvinyl alcohol solution in which a red dyecapable of absorbing light of 488 nm wavelength was dissolved dependingon the ratio of zero-order light 56 and first-order light 55 diffractedby the hologram in the photosensitive layer 32 to form an absorbinglayer 57 thereon. Following this, the adhesive agent, viz., theultraviolet curing adhesive agent 37 and the glass plate 41 acting as aspacer were placed on the absorbing layer 57, as in the firstembodiment. Then, the resultant multilayer structure was spun by meansof a spinner to spin an extra portion of the adhesive agent 37 out ofthe periphery thereof, so that the adhesive agent 34 layer was madeuniform, while the rpm of the spinner was controlled to obtain thedesired thickness, thereby laminating the glass plate 41 on theabsorbing layer 57 whereupon the adhesive agent 37 was cured byultraviolet irradiation thorough the glass substrate 31 or the glassplate 41. Finally, as in the first embodiment, the end product of highdiffraction efficiency could be obtained by the double-focus replicationprocess according to the arrangement of FIG. 3.

In this case, the absorbing layer 57 acts as follows. Usually, thezero-order light 56 is higher in intensity than the first-order light55, and so is less susceptible to efficient interference even when itinterferes with the latter in the photosensitive layer 52. However, theoptical path taken by the zero-order light 56 in the absorbing medium islonger than that by the first-order light 55, because the zero-orderlight 56 transmits obliquely through the absorbing layer 57 whereas thefirst-order light 55 transmits almost vertically as compared with thezero-order light 56. By control of the concentration and thickness ofthe absorbing layer 57, it is thus possible to decay the zero-orderlight 56 of higher intensity in a larger proportion and, hence, make thezero-order light 56 and first-order light 55 have substantially the sameintensity upon arrival at the photosensitive layer 52, so that they caninterfere with each other with high efficiency. It is thus possible toobtain replicas of high diffraction efficiency.

It is here noted that the absorbing layer 57 may be located between theglass plate 41 and the adhesive agent 37 or on the side of the glassplate 41 that faces away from the glass substrate 31, to say nothing ofthe FIG. 4 position.

Alternatively, it is acceptable to dispense with such an absorbing layer57. In this case, however, it is required to regulate the ratio of thezero-order light and the first-order light diffracted by the hologram inthe photosensitive material 32 to substantially 1:1 by somepost-exposure treatments of the photosensitive layer 32. For instance,when photopolymer HRF600X made by Du Pont is used, it is heat treated at120° C. for 2 hours after exposure to bring the diffraction efficiencyof the first-order light up to almost 100%. However, if this heattreatment is carried out at 120° C. for 10 minutes, it is then possibleto fix the diffraction efficiencies of the zero-order light andfirst-order light to substantially 50% and 50%, respectively. It is herenoted that by curtailing the post-exposure heat-treatment time asmentioned above, it is also possible to reduce changes in the angles ofinclination of interference fringes due to the deformation of thehologram photosensitive material which may occur by long-term heating,variations in the interference fringe plane, etc.

When the absorbing layer 57 is provided, it is possible to regulate theratio of the zero-order light and the first-order light to substantially1:1 by means of (1) thickness control of the absorbing layer 57, (2)control of heat-treatment conditions, (3) thickness control of thephotosensitive layer 32, etc. Particularly preferred control can beachieved by (1) combined with (3). In this case, it is possible todetermine the properties of the absorbing layer 57 in view of the ratioof the zero-order light and the first-order light after the posttreatment and, hence, gain more accurate control.

Regulation of the ratio of the zero-order light and the first-orderlight diffracted by the hologram in the photosensitive layer 32 tosubstantially 1:1 may also be achieved by reducing the thickness of thephotosensitive layer 32 in the absence of the absorbing layer 57. Forinstance, when photopolymer HRF600X made by Du Pont is used, thediffraction efficiency of the first-order light may be regulated tosubstantially 100% by an ordinary post treatment at a thickness of 4.0μm. However, if this thickness is reduced down to 2.0 μm, it is thenpossible to fix the diffraction efficiencies of the zero-order light andthe first-order light to substantially 50% and 50%, respectively.

In the aforesaid embodiments, an array comprising divergent elementholograms is used for the CGH array plate 21 so as to obtain a hologramarray of hologram plate 42 from the CGH array plate 21 by a contacthologram replication process. However, when a hologram array of hologramplate 42 is obtained from the CGH array plate 21 by the double-focusreplication process as in the case of FIG. 5, an array of collectiveelement holograms should be used for the CGH array plate 21.

The hologram plate and its fabrication process for achieving the firstobject of the present invention have been described with reference tothe first and second embodiments, respectively. Next, the hologram plateand its fabrication process for accomplishing the second object of thepresent invention are explained with reference to some embodiments.

FIGS. 5 to 10 are sectional views illustrative of a sequence of stepsfor carrying out the process for fabricating the hologram plateaccording to the first embodiment of the present invention for achievingthe second object thereof.

A plurality of holograms are fabricated from such a CGH plate (the firstplate) 7 as shown in FIG. 12 in one replication operation. To this end,a photopolymer or other photosensitive material layer 102, formed on asubstrate glass 101 of hologram size, is provided thereon with a PVA(polyvinyl alcohol) layer 103 acting as a combined protective layer andcoloring layer for preventing the occurrence of unnecessary interferencefringes due to multiple interferences to prepare a photosensitivematerial, as shown in FIG. 5. This hologram photosensitive material isbrought into close contact with the CGH array plate 7 or spaced awaytherefrom at a distance double the focal length f as shown in FIG. 12.Replicating illumination light (corresponding to the laser light 9 inFIG. 12) is entered into the resultant multilayer structure from the CGHplate 7 side in the case where the CGH plate 7 is of the transmissiontype, and the hologram photosensitive material side in the case wherethe CGH plate 7 is of the reflection type to allow transmitted light anddiffracted light in the case where the CGH plate 7 is of thetransmission type, and incident light and diffracted light in the casewhere the CGH plate 7 is of the reflection type to interfere in thephotosensitive material layer 102, thereby making a hologram replica ofthe CGH plate 7.

Then, as shown in FIG. 6, a thin sheet glass 105 is laminated on the PVAlayer 103 of each hologram photosensitive material with a hologramreplica of the CGH plate 7, using an optical adhesive agent 104, therebypreparing a plurality of unit hologram plates 120 having similarproperties. When the double-focus replication process is used in thiscase, the total thickness of the PVA layer 103, optical adhesive agent104 and thin sheet glass 105 should preferably be less than the focallength f.

Then, as shown in FIG. 7, a thin sheet glass 121 having a large area isbrought into vacuum contact with the optical flat surface of a referenceglass 130. When the double-focus replication process is used, thethickness of the thin sheet glass 121 should preferably be less than thefocal length f. Using an optical adhesive agent 122, a plurality of unithologram plates 120 in alignment are then laminated on the thin sheetglass 121 with the same force and height.

If, after the step of FIG. 6, the four side edge faces of the unithologram plates 120 are cut out by dicing or other cutting means, andespecially if the end faces of the substrate glass 101, photosensitivematerial layer 102, PVA layer 103, optical adhesive agent 104 and thinsheet glass 105 are cut out to put them in good alignment, air bubblesare less likely to penetrate in between adjacent unit holograms 120 atthe lamination step of FIG. 7, and alignment precision is furtherimproved.

Using an optical adhesive agent 124, a base glass 123 is bonded to theback sides of the unit hologram plates 120 put in alignment, as shown inFIG. 8, for the purposes of reinforcement and preventing penetration ofa solvent (an index matching liquid) in between adjacent unit hologramplates 120. Preferably in this case, the gap between adjacent unithologram plates 120 should be filled up with the optical adhesive agent124. This is because an unfilled gap between adjacent unit hologramplates 120 may possibly lead to unnecessary interference fringes due toreflection and scattering at that gap upon oblique incidence ofreplicating illumination light.

After the optical adhesive agent 124, etc. have been full-cured, thethin sheet glass 121 is desorbed and released from the reference glass130 brought into vacuum contact therewith, as shown in FIG. 10, so thata multifaceted hologram plate 125 of such shape in section as shown inFIG. 10 can be obtained in finished form according to one embodiment ofthe present invention.

With the multifaceted hologram plate 125 according to the presentinvention, all the unit holograms can be precisely replicated becausethe unit hologram plates 120 are kept flush with one another by onecommon thin sheet glass 121 provided over the unit hologram plates 120put in good alignment. When the hologram photosensitive material isbrought into close contact with the multifaceted hologram plate 125 withan index matching liquid applied therebetween for the purpose ofhologram replication, it is extremely unlikely that the optical adhesiveagent 122 between adjacent unit holograms 120 will be dissolved in theindex matching liquid (e.g., xylene) because the thin sheet glass 121 isprovided over the multifaceted hologram plate 125.

Fabricated by the lamination of only unit hologram plates 120 put ingood alignment with good properties, the multifaceted hologram plate 125according to the present invention have all unit hologram plates of goodquality and uniform properties, and so can be used for hologramreplication with high efficiency.

Regarding the aforesaid embodiment, it is noted that the PVA layer 103or thin sheet glass 105 may be omitted from the unit hologram plate 120.

It is also noted that the hologram to be replicated may be of either thetransmission or the reflection type, and that it is not always necessaryto replicate the multifaceted hologram plate 125 by the double-focusreplication process.

The hologram plate for achieving the third object of the presentinvention is now explained.

A transmission type hologram is recorded by entering object light andreference light in a hologram dry plate from the same side and allowingboth for interference in a hologram photosensitive material layer of thehologram dry plate. The thus recorded transmission type hologram or atransmission type computer-generated hologram (transmission type CGH)obtained by computing interference fringes by means of a computer, andrendering the interference fringes by means of electron beams to formthe interference fringes on a substrate by photolithography is used as atransmission type hologram plate. Another hologram dry plate is broughtinto close contact with or spaced slightly away from the side of thetransmission type hologram plate that faces away from the reconstructingillumination light incident side thereof. Replicating illumination lightcorresponding to the reconstructing illumination light is entered in theresultant multilayer structure from the hologram plate to allowdiffracted light corresponding to the object light and transmitted lightcorresponding to the reference light to interfere in the hologramphotosensitive material layer of the hologram dry plate, so that atransmission type hologram similar properties to the hologram plate isreplicated.

A reflection type hologram is recorded by entering object light andreference light in a hologram dry plate from opposite sides to allowboth to interfere in a hologram photosensitive material layer of thehologram dry plate. The thus recorded reflection type hologram is usedas a reflection type hologram plate. Another hologram dry plate isbrought into close contact with or spaced slightly away from the side ofthe reflection type hologram plate, on which reconstructing illuminationlight is incident. Replicating illumination light corresponding to thereconstructing illumination light is entered in the multilayer structurefrom the hologram dry plate side to allow diffracted light correspondingto object light and the replicating illumination light corresponding toreference light to interfere in the hologram photosensitive materiallayer of the hologram dry plate, so that a reflection type hologramsimilar in properties to the hologram plate is replicated.

The thus replicated transmission type hologram or reflection typehologram is used as a fresh hologram plate for similar replication,whereby a number of transmission or reflection type holograms havingsimilar properties can be fabricated.

However, such a hologram plate as mentioned above which, unlessotherwise stated, is understood to include both a transmission typehologram plate and a reflection type hologram plate—is susceptible tosurface marring, wearing and contamination as it is repeatedly used forreplication. Such defects are caused by repeated contact of the hologramplate with a hologram dry plate using a photopolymer or the like as ahologram photosensitive material or a spacer used in a hologramreplication process using such a spacer (FIGS. 12 and 13). For thisreason, a protective film is generally provided over the surface of thehologram plate. However, this protective layer, too, is damaged bymarring, wearing and contamination to such a degree that it can nolonger be used, as it is used over an extended period.

The third object of the present invention is to provide an easilyreleasable, hologram plate-protecting film for preventing surfacemarring, wearing and contamination which may otherwise occur in thecontact replication process or when foreign matters are removed. Oneembodiment of the present invention in this regard is now explained.

FIG. 11 is a sectional view of how to replicate a transmission typehologram using the hologram plate according to this embodiment. Astypically set forth in JP-A's 11-6917 and 11-271535, a hologram plate210 is prepared by forming a metal film 202 formed of Cr on atransparent substrate 201 and using electron beams to patterninterference fringes for a hologram color filter as an example by meansof photolithography, thereby forming an amplitude typecomputer-generated hologram pattern 205 thereon.

Then, the metal film 202 with such an amplitude type computer-generatedhologram pattern 205 formed thereon is provided thereon with a firstlayer 203 capable of being removed by water or a solvent according tothe present invention. Finally, the first layer 203 is provided thereonwith a second layer 204 formed of a curing resin capable of being curedby light or heat. In this way, the transmission type hologram plate 204according to the present invention is fabricated.

In this embodiment, the second layer 204 formed on the surface of thehologram plate 210—which surface comes into close contact with ahologram dry plate 220 or the like functions as a protective layer forthe finely patterned hologram layer 202, thereby preventing the marring,wearing and contamination of the hologram layer 202, which may otherwiseoccur at steps of coating an index matching liquid, carrying out contactreplication, removing the index matching liquid, removing foreignmatters, and so on.

The light or heat-curable resin layer 204 is usually of high hardness.However, as many holograms are replicated, the protective layer 204,too, is subjected to marring, wearing and contamination at the steps ofcoating an index matching liquid, carrying out contact replication,removing the index matching liquid, removing foreign matters, and so on.

In this case or, for instance, when one fails to form the first layer203 or the second layer 204, the hologram plate 210 is washed with wateror boiled in boiling water, so that the protective layer 204 can beeasily removed because the first layer 203 is dissolved in water orboiling water. Then, if fresh first and second layers 203 and 204 areprovided on the hologram layer 202, the hologram plate 210 can then beregenerated.

This embodiment of the present invention is now explained with referenceto one specific example. A hologram plate 210 was prepared by forming anabout 0.05 μm thick Cr film 202 on a quartz substrate 201 (n=1.46) andrendering and patterning interference fringes for a color filter bymeans of photolithography using electron beams to form a hologrampattern 205.

On the other hand, 0.8% by weight of a red dye (Kayafect Red G.C.I.Direct R-23, Nippon Kayaku Co., Ltd.) wad added to and dissolved in a10% (solid content) aqueous solution of polyvinyl alcohol to prepare acolored aqueous polyvinyl alcohol solution. By means of spin coating,this aqueous solution was coated on the Cr film 202 of the hologramplate 210 with the hologram pattern 205 formed thereon, and then driedat room temperature for 1 hour and 70° C. for a further 1 hour to obtaina light absorbing layer 203 of about 1 μm in thickness. This lightabsorbing layer 203 had a refractive index of n=1.52.

Then, an ultraviolet curing resin (Seikabeam EXG-75-1, Dainichi SeikaIndustries, Ltd.) was coated on the light absorbing layer 203 by meansof spin coating, then dried at 60° C. for 1 hour, then irradiated with2,000 mJ ultraviolet radiation from an ultraviolet lamp including allwavelength components 250 nm, 330 nm and 360 nm to cure the resin, andfinally dried at 70° C. for 2 hours to bring the formation of aprotective layer 204 of about 2 μm in thickness to completion. Theultraviolet-cured resin layer 204 had a refractive index of n=1.53.

The thus fabricated hologram plate 210 was used for the replication of ahologram color filter in the arrangement of FIG. 11. To this end, ahologram dry plate 220 is prepared by laminating a hologramphotosensitive material layer 222 comprising a photopolymer on atransparent substrate 221 and laminating a protective layer 223 on thesurface of the layer 222. The protective layer 204 of the hologram plate210 is brought into close contact with the protective layer 223 of thehologram dry plate 220 with an index matching liquid 215 interleavedtherebetween while a prism 211 having an inclined surface 212 is broughtinto close contact with the back surface of the hologram plate 210.Laser light of 514 nm wavelength is entered in the inclined surface 212to enter replicating illumination light 230 in the hologram layer 202 ofthe hologram plate 210 at a large angle of incidence.

Zero-order transmitted light 231, first-order diffracted light 232 andsecond-order diffracted light 233 are generated from the hologrampattern 205. However, the zero-order transmitted light 231 andsecond-order diffracted light 233 are higher in attenuation factor thanthe first-order diffracted light 232, because the first-order diffractedlight 232 is almost vertical with respect to the hologram layer 202whereas the zero-order transmitted light 231 and second-order diffractedlight 233 have a large angle of diffraction with respect to the hologramlayer 202 and so the length of an optical path passing through the lightabsorbing layer 203 becomes relatively long with respect to thezero-order diffracted light 231 and second-order diffracted light 233.Of the zero-order transmitted light 231, first-order diffracted light232 and second-order diffracted light 233, the zero-order transmittedlight 231 has the highest light intensity and the second-orderdiffracted light 233 has the lowest light intensity. Through the actionof this light absorbing layer 203, it is thus possible to make theintensities of the zero-order transmitted light 231 and first-orderdiffracted light 232 substantially equal to each other upon arrival atthe hologram photosensitive material layer 222 of the hologram dry plate220 and, hence, reduce the relative intensity of the second-orderdiffracted light 233 extremely. Thus, the insertion of the lightabsorbing layer 203 in the hologram plate 210 makes unnecessaryinterference fringes due to the second-order diffracted light 233unlikely to occur. The zero-order transmitted light 231, first-orderdiffracted light 232, second-order diffracted light 233, etc. attenuatedthrough the light absorbing layer 203 are again incident on the hologramlayer 202 after Fresnel reflection at interfaces of the hologram dryplate 220 (the surface of the protective layer 223, the interfacebetween the protective layer 223 and the hologram photosensitivematerial layer 222, the interface between the hologram photosensitivematerial layer 222 and the transparent substrate 221, and the backsurface of the transparent substrate 221). However, the reflected lightis attenuated through the light absorbing layer 203 and its lightintensity is sufficiently reduced upon arrival at the hologramphotosensitive material layer 222. Thus, unnecessary interferencefringes due to the reflected light from these interfaces, too, areunlikely to occur because of the presence of the light absorbing layer203.

The zero-order transmitted light 231 and first-order diffracted light232 generated from the hologram plate 210 interfere in the hologramphotosensitive material layer 222 of the hologram dry plate 220, so thata transmission type hologram similar in diffraction properties to thehologram plate 210 is replicated in the hologram dry plate 220.

A hologram plate with no protective layer provided thereon issusceptible to marring. For instance, a fine patterning (205) brokendown in the process of about 500 replication cycles. However, a hologramplate with such a protective layer 204 provided thereon according to thepresent invention could stand up to 10,000 or more replication cycles.This protective film, even when more or less damaged, had no adverseinfluence on replication because the refractive index of the ultravioletcuring resin layer 204 was nearly equal to that of the index matchingliquid 215 (cardinal oil; n=1.515). Removal of the protective layer 204is achieved by placing and boiling the hologram plate 210 in boilingwater to dissolve the light absorbing layer 203 therein. The merit ofthis method is that no access to the patterned surface 205 is needed. Byremoving and regenerating the protective layer 204 per 10,000replication cycles, the hologram plate 210 could be protected on asemi-permanent basis.

While the hologram plate for achieving the third object of the presentinvention has been described with reference to its specific embodimentand example, it is understood that the present invention is not limitedthereto, and so many modifications may be made. The hologram plate ofthe present invention is applicable to not only the transmission typebut also the reflection type. It is also understood that the first layer203 capable of being removed by water or a solvent and the second layer204 provided thereon and formed of a curing resin capable of being curedby light or heat can be provided on not only the amplitude type hologramlayer with a metal film patterned thereon but also a hologram layercomprising a photopolymer or other hologram photosensitive materiallayer with interference fringes recorded therein.

It is not always necessary to provide such layers directly on thehologram layer 202. In the replication process using a spacer forinstance, the first layer 203 capable of being removed by water or asolvent and the second layer 204 provided thereon and formed of a curingresin capable of being cured by light or heat may be formed on thesurface of the spacer.

While the hologram plate and its fabrication process of the presentinvention have been described with reference to some specificembodiments, it is understood that the present invention is not limitedthereto, and so many modifications may be made.

In the present invention for the purpose of achieving the aforesaidfirst object, the hologram plate comprises a multilayer structure madeup of a first transparent substrate, a hologram layer, an adhesive layerand a second transparent layer and the second transparent substratedefines a surface in contact with a hologram photosensitive materialduring hologram replication, so that the second transparent substratecan function as a protective layer to make the hologram plate resistantto marring. In addition, the second transparent substrate can be used asa spacer for the double-focus replication process wherein the distancebetween the hologram plate and the hologram photosensitive material isset at substantially double the focal length of each collective elementhologram, so that replicas can be fabricated with constant focallengths.

An absorbing layer is located between the hologram layer and theadhesive layer or at other position to allow the zero-order light andfirst-order light diffracted by the hologram layer to have substantiallythe same intensity, so that hologram replicas of high diffractionefficiency can be obtained.

According to the present invention for achieving the aforesaid secondobject, all the unit holograms can be precisely replicated because theunit hologram segments are kept flush with one another by one commonthin sheet glass provided over the plurality of juxtaposed unit hologramsegments. When the hologram photosensitive material is brought intoclose contact with the multifaceted hologram plate with an indexmatching liquid applied therebetween for the purpose of hologramreplication, it is extremely unlikely that an optical adhesive agentbetween adjacent unit hologram segments will be dissolved in the indexmatching liquid. If a glass sheet is used as the transparent thin sheet,improved durability is then obtained. Fabricated by the lamination ofonly unit hologram segments put in good alignment with good properties,the multifaceted hologram plate according to the present invention forachieving the aforesaid second object have all unit hologram segments ofgood quality and uniform properties, and so can be used for hologramreplication with high efficiency.

According to the present invention for achieving the aforesaid thirdobject, there is provided a hologram plate comprising a hologram layerwith interference fringes formed thereon, a first layer capable of beingremoved with water or a solvent, which is provided on the surface ofsaid hologram layer or a transparent layer formed thereon, and a secondlayer of a curing resin capable of being cured by light or heat, whichis formed on said first layer. The second layer functions as aprotective layer for the hologram layer thereby preventing the marring,wearing and contamination of the hologram layer, which may otherwiseoccur at steps of coating an index matching liquid, carrying out contactreplication, removing the index matching liquid, removing foreignmatters, and so on. As many holograms are replicated, the second layer,too, is subjected to marring, wearing and contamination. In this caseor, for instance, when one fails to form the first layer or the secondlayer, the hologram plate is washed with water or boiled in boilingwater, so that the protective layer can be easily removed. Then, iffresh first and second layers are provided on the hologram layer, thehologram plate can be regenerated.

The hologram plate for achieving the third object of the presentinvention comprises a hologram layer with interference fringes formedthereon, a first layer capable of being removed with water or a solvent,which is provided on the surface of said hologram layer or a transparentlayer formed thereon, and a second layer of a curing resin capable ofbeing cured by light or heat, which is formed on said first layer. Thesecond layer functions as a protective layer for the hologram layer,thereby preventing the marring, wearing and contamination of thehologram layer, which may otherwise occur at steps of coating an indexmatching liquid, carrying out contact replication, removing the indexmatching liquid, removing foreign matters, and so on. As many hologramsare replicated, the second layer, too, is subjected to marring, wearingand contamination. In this case or, for instance, when one fails to formthe first layer or the second layer, the hologram plate is washed withwater or boiled in boiling water, so that the protective layer can beeasily removed. Then, if fresh first and second layers are provided onthe hologram layer, the hologram plate can be regenerated.

What we claim is:
 1. A hologram plate comprising: a plurality ofjuxtaposed unit hologram segments, each unit segment comprising areplication of a single master hologram, wherein: one common transparentthin sheet is provided over the surfaces of said plurality of juxtaposedunit hologram segments with an adhesive agent interleaved therebetween,and each said unit segments is physically independent of other of saidplurality of unit hologram segments.
 2. The hologram plate according toclaim 1, wherein each unit hologram segment comprises a transparentsubstrate, a photosensitive material layer formed thereon while ahologram is recorded therein, and a protective layer formed on saidphotosensitive material layer.
 3. The hologram plate according to claim2, wherein a transparent thin sheet is bonded onto said protective layerfor each unit hologram segment.
 4. The hologram plate according to anyone of claims 1 to 3, wherein said plurality of unit hologram segmentsare hologram segments replicated from the same hologram plate.
 5. Thehologram plate according to any one of claims 1 to 3, wherein each unithologram segment comprises a hologram color filter.
 6. The hologramplate as set forth in claim 1, wherein said plurality of unit hologramsegments are physically juxtaposed.
 7. A process for fabricating ahologram plate comprising a plurality of juxtaposed unit J hologramsegments, each unit segment comprising a replication of a single masterhologram, and one common transparent sheet provided over the surfaces ofsaid unit hologram segments with an adhesive agent interleavedtherebetween, which comprises the steps of: preparing a plurality ofunit hologram segments, adsorbing a transparent thin sheet onto thesurface of a reference plate and laminating said plurality of unithologram segments, in juxtaposed relation to each other, on saidtransparent thin sheet with an adhesive agent interleaved therebetween,bonding a base plate onto the back side of said plurality of juxtaposedunit hologram segments with an adhesive agent interleaved therebetween,and desorbing said transparent thin sheet from said reference plate torelease said transparent thin sheet from said reference plate, whereineach said unit segments is physically independent of other of saidplurality of unit hologram segments.
 8. The hologram plate fabricationprocess according to claim 7, wherein at the step of preparing aplurality of unit hologram segments, said plurality of unit hologramsegments are hologram segments replicated from the same hologram plate.9. The process for fabricating a hologram plate as set forth in claim 7,wherein said plurality of unit hologram segments are physicallyjuxtaposed.